As in CN 200720153070, the clamping force is purely derived from a simple active wedge that moves vertically to push against the passive wedge outwards to clamp against the pile. Unlike the present invention, the clamping force around the pile is not solely derived from the vertical hydraulic clamps but also further resisted by the jamming action of the clamp wedges against the circular clamp housing in response to the externally applied vertical pile driving force. In addition, for unsymmetrical wedge clamping mechanism it would be obvious that unless the active wedge contact is exactly at the centre of the passive wedge, the clamping pressure distribution on to the pile would be trapezoidal and non-uniform. However in the present innovation, if the pile's alignment remains vertical, the top and bottom circular clamp housing will make contact at two equidistant contact point from the centre of the clamps wedge to ensure that uniform pressure will result irrespective of the contact positions of the clamp wedges. Further, the clamping jaws in CN 200720153070 are released by moving the active wedge upwards but the clamping jaws do not retract unlike the current spring loaded clamp wedges.
As in CN2608559Y, although there is a top and bottom wedges, individually the clamp wedge is unsymmetrical and therefore would cause non-uniform clamping pressure as stated earlier. The curvature radius of the contact surface of the clamp wedge is larger than the device box therefore the sides of the clamp wedge is contact with the device box and there will be no rotational play of the wedge in the plan view, which means that the clamps will only grip the pile squarely and vertically. Unlike the present invention, the clamp wedges can swivel within 3 degrees in the horizontal and vertical axis like a “ball and socket” joint inside the circular clamp housing to accommodate the tilt and twist of the pile. Another advantage in the present invention is that the top and bottom circular housing moves in tandem in the opposite directions under a action and reaction force applied by the vertical hydraulic clamp while the clamp wedges are held vertically stationary with respect to the pile, therefore the lower vertical hydraulic clamps can be omitted to save costs, whereas in CN2608559Y all the individual clamps wedges are forced outwards independently for the top and bottom vertical clamps.
CNO3223773.1 uses two adjacent clamp return springs to open the non-swivelling clamp by extending and compressing the spring along the axis of the spring. However apart from allowing the spring to expand and contract along the its axis, the present invention must also allow unrestricted lateral displacement of the spring perpendicularly to the axis of the spring caused by twisting of the adjoining clamp wedges. This is achieved by placing the spring centrally to minimise the twists and allow free movements of the spring within a bell shaped hollow cavity.